The power generator has been widely used by the people doing all walks of life. With the battery-free trend being accepted, the design of compact high efficiency power generator has become an important field of interest. Compact power generating devices can be used as a power supply for portable electronic products. Therefore, generating sufficient power with reasonable cost in limited space has become a key issue to make these compact portable power generating devices widely adopted. These compact power generating devices can be installed in/on wearable portions such as the pockets, the shoes, the glasses and the watch for emergent power requirements by, such as, illumination, radio and communication devices. The reciprocating handpower flash light has been developed with low power efficiency. The magnetic power generators can be divided into continuous rotary, oscillating, and reciprocating power generators according to the movement of the active cells. Some reciprocating power generators are designed to be flat due to the spatial limitation. However, to provide sufficient power, the currently used pipe reciprocating linear power generators are spatially efficientless because they are not flat.
Taking permanent magnet power generators or excited power generators for example, if the active cell is disposed inside the winding and is a multi-pole magnetized magnet or is multi-pole magnetic flux distributed by claw-pole magnetic conductance, the winding axis of each of the windings is generally parallel with the direction of the magnetic pole, which results in gaps between the wings to reduce the winding density and shorten the effective winding length. The gaps are generally filled with silicon steel core, causing the cogging force. The power density of a power generator is related to the number of windings in the effective magnetic region. For low speed magnetic power generator with limited speed or displaced stroke, it is important to increase the power density of the power generator at a low speed.
For a reciprocating linear power generator as shown in FIG. 1, the stroke of the active cell 10 is required to be twice the length of the winding 12 so that the winding 12 corresponds to the maximum induced output voltage. Furthermore, the intensity variation of magnetic flux along each turn of the winding 12 is large, it is possible that the efficiency of power conversion between electricity and kinetic energy can be further improved under the same input energy.
For a symmetric linear motor/power generator (as shown in FIG. 2A, FIG. 2B and FIG. 2C, wherein FIG. 2A is a side view, FIG. 2B is a top view, and FIG. 2C is an enlarged view of the winding), the winding 22 is disposed in the center of the magnet. Inspecting the effective length of each turn of the winding 22 from the viewpoint of magnetic flux as shown in FIG. 2C, the effective induced electromotive force is generated on the L2 portion, while the L1 portion in parallel with the magnetic flux is neglected. Therefore, compared to the winding around the magnet, the symmetric linear motor/power generator has poor magnetic force to length ratio, and lengthened conductive wires lead to increased cost and higher internal resistance.